tlc: Sprint 3 C9 — empty pattern inverts/clears marks

Previously mark_pattern("") and unmark_pattern("") were silent
no-ops (glob_match returned false for empty pattern). Now they
match MC's behavior:
  - mark_pattern(""): calls reverse_marks() (toggles every
    entry; from 0 marks → all entries marked, vice versa)
  - unmark_pattern(""): clears all marks

Tests (2 new in panel::tests):
  - mark_pattern_empty_inverts_marks (0→2→0 cycle)
  - unmark_pattern_empty_clears_all_marks

Total: 1276 passing (was 1274; +2 new).

local/recipes/tui/tlc/source/src/filemanager/panel.rs

@@ -424,8 +424,14 @@ impl Panel {
         }
     }
 
-    /// Mark entries matching `pattern` (Unix glob).
+    /// Mark entries matching `pattern` (Unix glob). An empty pattern
+    /// marks every regular entry (skipping `..`), matching MC's
+    /// "Select group" behavior with an empty expression.
     pub fn mark_pattern(&mut self, pattern: &str) {
+        if pattern.is_empty() {
+            self.reverse_marks();
+            return;
+        }
         for e in &self.entries {
             if glob_match(pattern, &e.name) {
                 self.marked.insert(e.name.clone());
@@ -433,8 +439,14 @@ impl Panel {
         }
     }
 
-    /// Unmark entries matching `pattern` (Unix glob).
+    /// Unmark entries matching `pattern` (Unix glob). An empty
+    /// pattern clears every mark (matching MC's "Unselect group"
+    /// with an empty expression).
     pub fn unmark_pattern(&mut self, pattern: &str) {
+        if pattern.is_empty() {
+            self.marked.clear();
+            return;
+        }
         let to_remove: Vec<String> = self
             .entries
             .iter()
@@ -1238,6 +1250,40 @@ mod tests {
         let _ = fs::remove_dir_all(&dir);
     }
 
+    #[test]
+    fn mark_pattern_empty_inverts_marks() {
+        let dir = std::env::temp_dir().join("tlc-panel-mark-empty-test");
+        let _ = fs::remove_dir_all(&dir);
+        fs::create_dir_all(&dir).unwrap();
+        fs::write(dir.join("a.txt"), b"x").unwrap();
+        fs::write(dir.join("b.txt"), b"x").unwrap();
+        let mut p = Panel::new(&dir, &empty_cfg()).unwrap();
+        // Empty pattern inverts: from 0 marks → all entries marked
+        // (skipping '..').
+        p.mark_pattern("");
+        assert_eq!(p.marked_count(), 2);
+        // Apply again: 2 marks → 0 marks.
+        p.mark_pattern("");
+        assert_eq!(p.marked_count(), 0);
+        let _ = fs::remove_dir_all(&dir);
+    }
+
+    #[test]
+    fn unmark_pattern_empty_clears_all_marks() {
+        let dir = std::env::temp_dir().join("tlc-panel-unmark-empty-test");
+        let _ = fs::remove_dir_all(&dir);
+        fs::create_dir_all(&dir).unwrap();
+        fs::write(dir.join("a.txt"), b"x").unwrap();
+        fs::write(dir.join("b.txt"), b"x").unwrap();
+        let mut p = Panel::new(&dir, &empty_cfg()).unwrap();
+        p.mark_pattern("*.txt");
+        assert_eq!(p.marked_count(), 2);
+        // Empty pattern clears every mark.
+        p.unmark_pattern("");
+        assert_eq!(p.marked_count(), 0);
+        let _ = fs::remove_dir_all(&dir);
+    }
+
     #[test]
     fn test_is_archive_extension_tar() {
         assert_eq!(is_archive_extension("foo.tar"), Some("tar"));